Analysis: Because the diamond is also a parallelogram and B is a subset of A, A ∪ B = A = {x | x is a parallelogram},

A ∩ b = b = {x | x is a diamond}

Empty set: A set without any elements becomes an empty set.

Finite set: A set with finite elements is called a finite set.

Infinite set: A set with infinite elements is called an infinite set.

Because of x? +1=0 cannot be established, that is, there is no solution, {x | x? +1 = 0} contains no elements, so {x | x? +1 = 0} is an empty set.

Because of x? -2x-3=0, that is, (x+ 1)(x-3)=0, so x=- 1 or x=3, so {x | x? -2x-3 = 0} = {- 1, 3} is a finite set.

Because x∈R, y∈R, {(x, y) | x ∈ r, y ∈ r} is a set of all points on a plane, so {(x, y) | x ∈ r, y ∈ r} is an infinite set.

Satisfied, please adopt! Thank you!